The photoautotrophic growth of microorganisms or cells is enabled by the photosynthetic capacity of the chlorophyll-containing microorganisms or cells, whereby carbon dioxide (CO2), through photosynthetic carbon fixation, serves as the carbon (or food) source. Photoautotrophic growth requires the presence of light for photosynthesis to occur. A steady supply of CO2 when light is available also promotes culture growth.
By contrast, heterotrophic growth takes place when the microorganisms or cells, in the absence of photosynthetic CO2 fixation, rely on exogenous carbon-based molecules, typically sugars such as glucose or sucrose, present in the liquid culture medium as their carbon (or food) source. Heterotrophic growth necessitates a sterile or axenic growth environment to avoid culture contamination; otherwise, unwanted and competing bacteria and other microorganisms would grow in the culture owing to the presence of the carbon-based food source. This mode of growth also requires a steady supply of oxygen (O2) which the microorganisms or cells need as they breakdown the carbon-based molecules through the process of respiration. Since light is not essential, heterotrophic production is generally carried out in darkness. Mixotrophic growth takes place when the microorganisms or cells grow both photoautotrophically and heterotrophically.
Commercial large-scale production of microalgae began in the late 1960s in Japan then spread throughout the world in the 1970s and 1980s. In recent years the number of commercial large-scale facilities around the world has increased at nearly exponential rate as demand for animal feed, nutraceuticals, vitamins and lipids, biofuels and bioplastics has increased. As natural resources become increasingly scarce it is evident that the need for large-scale commercial production of microalgae and other cell types will also grow.